1. Field of the Invention
The present invention concerns a magnetic resonance system with a number of components including a basic magnetic field generation unit, gradient coils as well as a radio-frequency coil arrangement. The components are thereby respectively controllable according to a control sequence via at least one digital module and at least one analog module, and the analog modules are arranged external to a control computer controlling the digital modules. Moreover, the invention concerns a method for the operation of such a magnetic resonance system.
2. Description of the Prior Art
Magnetic resonance tomography is a widespread method to acquire images of the inside of a body. In this method the body to be examined is exposed to a relatively high basic magnetic field, for example of 1.5 Tesla, or even of 3 Tesla in newer systems, known as high magnetic field systems. A radio-frequency excitation signal (known as the B1 field) is then emitted with a suitable antenna device, which causes the nuclear spins of specific atoms excited to resonance by this radio-frequency field are tilted by a specific flip angle relative to the magnetic field lines of the basic magnetic field. The radio-frequency signal radiated during the return of the nuclear spins to equilibrium (known as the magnetic resonance signal) is then detected with suitable antenna devices (which can also be the same as the transmission antenna device). The raw data acquired in this manner are used in order to reconstruct the desired image data. For spatial coding, defined magnetic field gradients are superimposed on the basic magnetic field during the transmission and the readout or acquisition of the radio-frequency signals.
Such magnetic resonance systems have a number of components that must be controlled under consideration of fixed time correlations within a predetermined measurement sequence in the framework of a measurement procedure. Among these components are, for example: the aforementioned basic magnetic field generation unit that serves to generate the basic magnetic field; the gradient coils that are used to generate the magnetic field gradients; and the radio-frequency coil arrangement, which normally has multiple radio-frequency coils for the transmission and/or acquisition of the radio-frequency signals. All of these components are typically operated in analog fashion, but the control ensues digitally. Therefore at least one digital module and at least one analog module are normally required in the control path to these components.
For the exemplary case of the radio-frequency coil arrangement, differentiation must be made between transmission modules and acquisition modules. Among other things, a radio-frequency amplifier is necessary in the transmission branch, this radio-frequency amplifier converting a radio-frequency signal previously generated in a digital transmission module into the analog radio-frequency signal to be emitted at the antenna. This signal must provide a sufficient radiating power. For signal acquisition, the received signal is initially demodulated with suitable electronics in an analog acquisition module and is converted by an A/D converter into a digital acquisition signal. This is sent to a digital acquisition module which digitally further demodulates and processes the digital signal. At present, known acquisition modules can processes a specific number of acquisition channels, meaning that they can demodulate and further process signals from a specific number of individual antennas. The signal of a frequency generation unit (usually an NCO—Numerical Controlled Oscillator), which supplies a suitable intermediate frequency, is necessary both at the transmission side (i.e. for the generation of the radio-frequency signal by the digital modulators) and at the acquisition side for digital demodulation.
Since it is essential for the measurement that the predetermined schedule of the emission of the individual signals (for example the radio-frequency signals, the gradient pulses and the readout commands) matched to one another must be precisely maintained, and for this each component must implement a very specific action at a precisely determined time, a central control concept has conventionally been used in which the various digital modules are integrated into the control computer. With the use of the system clock of the control computer and, if necessary, a clock or a timestamp, it is then possible to establish the synchronicity and isochronicity among the individual components. The digital modules are thereby typically fashioned as modules that can be connected to a bus within the control computer. With this centrally organized control system, a future maximum expansion must already be taken into account in the design since the capacities of the central control computer are limited both spatially and with regard to power. This means, for example, that whether additional transmission coils or reception coils are possibly to be added must be taken into account in the planning of the system. This maximum expansion, however, cannot be exactly planned for all system functionalities at the point in time of the design since the technical developments advance quickly. Therefore, it frequently occurs that current controls are presently either less-than-fully occupied or, in a disadvantageous case, that bottlenecks exist since existing expansion capabilities are not sufficient.
To solve this problem, a few niche solutions are known. For example, it has been proposed to realize a clone concept at the excitation side in which the control computer is present in multiple instances, and one of the control computers is wired as a master and the others as clients. This solution is technically very complicated and uneconomical and deals only with a partial aspect of one component, namely the transmission side. Such an individual solution is also known for the acquisition side, wherein ultimately a bus expansion offloaded from the control computer is proposed. However, a complete and economic solution of the problem does not exist with this either. Added to this, not only must exact time workflows be synchronized between the individual components among one another and the control computer, but also high data rates must be transferred (for example, the precise information about pulse sequences to be emitted at the transmission side, in particular, a number of precise envelopes for the radio-frequency pulses and/or gradient pulses), and a significant number of acquired measurement raw data at the acquisition side.